CVE-2026-49283: Simplesamlphp SAML2

High severity, CVSS 8.7. EPSS: 0.5% chance of exploitation in the next 30 days.

The SimpleSAMLphp SAML2 library is a PHP library for SAML2 related functionality. Prior to versions 4.19.3, 4.20.2, 5.0.6, and 6.2.1, the HTTPArtifact::receive() flow can treat an unsigned embedded SAML Response as cryptographically valid for the wrong identity provider. SOAPClient::addSSLValidator() attaches a TLS-based validator to the outer SOAP ArtifactResponse, while the embedded Response receives a validator that delegates to the outer message and is later checked against metadata selected from the embedded response issuer rather than necessarily the artifact issuer. SOAPClient::validateSSL() returns normally when the TLS public key does not match the key being validated, and SAML2\Message::validate() treats a validator call that does not throw as successful. In a multi-IdP federation, a malicious or lower-trust IdP can therefore provide an ArtifactResponse containing an unsigned Response that claims a higher-trust victim IdP as issuer and authenticate as arbitrary users with attacker-chosen assertion attributes, NameID, and session data. This issue is fixed in versions 4.19.3, 4.20.2, 5.0.6, and 6.2.1.

Affected products

• Simplesamlphp SAML2: before 4.19.3 (fixed in 4.19.3); from 4.20.0, before 4.20.2 (fixed in 4.20.2); from 5.0.0, before 5.0.6 (fixed in 5.0.6); from 6.0.0, before 6.2.1 (fixed in 6.2.1)

Published 2026-08-19. Last modified 2026-09-18.